The invention relates to a device for controlling the quantity of secondary combustion air in coke oven chambers of a coke oven battery of the “Heat-Recovery” or “Non-Recovery” type, wherein this device regulates the air volume through a parallelepiped attachment or a plate driven by a positioning motor so that this device can be regulated, for example, via a control mechanism which depends on measuring values in a coke oven chamber. Heating of a coke cake of a coke oven battery can be substantially homogenized and improved via the secondary heating space located under the coke cake. The quantity of secondary air can be supplied by the inventive device in several quantity graduations, if required. A supply of secondary air in multiple stages allows for reducing the quantity of formed nitric oxides substantially. The present invention also relates to a method for proportioning of secondary combustion air in a coke oven chamber.
Based on prior art in technology, the heating of coke oven chambers is so executed that the heating of a coke cake is performed as evenly as possible from all sides and that the quality of coke thus obtained is improved in this manner. For coal carbonization, the pre-warmed coking chamber of the coke oven is charged with a coal layer and then closed. The coal layer can be provided as a top-filled coal batch or in compacted, stamped form. By warming the coal, volatile matter contained in coal, above all hydrocarbons and hydrogen, is given off and expelled. Further heat generation in the coking chamber of “Non-Recovery” coke ovens and “Heat-Recovery” coke ovens is exclusively effected by combustion of released coal volatile matter constituents which degas successively as heating advances.
According to prior art in technology, combustion is so controlled that part of the gas released which is also designated as crude gas is burnt directly above the coal charge in the coking chamber. Combustion air needed for this purpose is sucked in through apertures in the doors or ceiling or through apertures in the doors and in the ceiling. This combustion stage is also designated as the first air stage or primary air stage. The primary air stage usually does not lead to complete combustion. Heat released on combustion heats the coal layer, with an ash layer forming on its surface after a short period of time. This ash layer provides for sealing towards air and in the further course of the coal carbonization process, it prevents a burn-off of the coal layer. Part of the heat released on combustion is predominantly transferred by radiation into the coal layer. A mere heating of the coal layer from the top by applying only one air stage, however, would lead to uneconomically long coking times.
Crude gas partly burnt in the primary air stage is therefore burnt at another stage, with the heat thus evolving being supplied to the coal layer from the bottom or from the side. This post-combustion designated as secondary combustion usually occurs in so-called secondary heating spaces located underneath the coke oven chamber and underneath the coke cake, so that partly burnt coking gas completely burns-out there, while the heat of combustion evolving there heats the coke cake from below. Thereby the heat distribution of the coke cake is substantially homogenized from all sides and the quality of coke produced is noticeably improved. Guiding of partly burnt coking gas is usually taken charge of by so-called “downcomer” channels which for example are located in the lateral brickwork of a coke oven chamber.
According to this approach, air needed for secondary air combustion, which is called secondary air, is supplied through so-called secondary air apertures located underneath the lateral coke oven chamber doors of coke oven chambers in a typical construction style. From there, the secondary air streams into a so-called secondary air sole where the air is collected and conducted into a secondary heating chamber located above. Secondary combustion occurs there. Combustion air streaming in is generally supplied in a clearly over-stoichiometrical quantity. Thus it is ensured that the partly burnt coking gas burns-out completely, so that the heat of combustion contained therein is completely given off. In this manner, it is also intended to prevent a discharge of incompletely burnt carbonization products, e.g. hydrocarbons.
Supplied secondary air, however, has generally attained the temperature of the surrounding atmosphere, thus quite substantially reducing the temperature of the secondary air sole and secondary heating space underneath the coke cake. By a non-controlled supply of secondary combustion air into the secondary heating space, the temperature of the secondary heating space cannot be controlled, so that the temperature of the secondary heating space may clearly differ from the temperature in the primary heating space, which is also designated as coke oven vault. As a result, the heating of coke from different sides is uneven. Moreover, the quantity of supplied secondary air cannot be regulated depending on the amount of oxygen in the secondary heating space. This may entail a formation of pollutants, but more particularly a formation of non-burnt hydrocarbons or nitric oxides of the NOx type.
WO 2007/057076 A1 describes a ventilating device for the supply of primary and secondary air for the combustion of coking gas from coke ovens built in flat construction style and arranged as a battery, said ventilating device being comprised of at least one venting aperture per coking chamber for the primary air, said venting aperture extending through the relevant coke oven door or through its framing wall, and furthermore comprised of at least one venting aperture per coking chamber for the secondary air and movably supported closure elements being provided at least for a part of the venting apertures, wherein according to the invention at least a part of said closure elements of the venting apertures is mechanically connected to a positioning element which is controlled and driven from a central position, and wherein the closure elements are to be actuated by means of the positioning element depending on the demand for combustion air, with it being possible to establish the mechanical connection of each closure element to the central positioning element individually; in particular it is possible to effect the starting position of each individual closure element at the beginning of the carbonization cycle of the associated coking chamber separately and independently of the other closure elements of the neighboring coking chambers. Embodiments lay claim to the closure elements, positioning elements, and to the method.
The procedure is not automatized and frequently it is controlled by temperature-sensitive chains extending around a coke oven. Prior art devices frequently comprise positioning elements or closure elements which yield only a limited service life if exposed to high temperatures of coke ovens.